1. Field of the Invention
The present invention relates to transaxle units of motor vehicles in general, and more particularly to a transaxle unit provided with an integrated power take-off unit and torque-coupling device.
2. Description of the Prior Art
Recently, there has been a significant increase in the demand for all-wheel-drive (AWD) motor vehicles equipped with a powertrain capable of providing drive torque to all four wheels. Traditional AWD vehicles are equipped with a longitudinally-extending engine and transmission that deliver power to the input of a transfer case which, in turn, distributes the power to front and rear drive axles. As is known, some transfer cases are equipped with a transfer clutch for automatically transferring power to the front drive axle during lost traction situations to establish an “on-demand” all-wheel drive mode. Other transfer cases are equipped with an interaxle differential which functions to transmit power to both drive axles during normal conditions at a predetermined torque distribution ratio so as to establish a full-time all-wheel drive mode. Such AWD vehicles are typically based on a rear wheel drive arrangement and, as such, are generally limited to SUV's and trucks.
To provide drive torque to the rear wheels in front-wheel-drive (FWD) motor vehicles, a front-wheel drive transaxle has to be modified by adding a power take-off unit (PTU) driven by the output of the FWD transaxle and supplying power to the rear drive axle. Moreover, it is desirable to provide the FWD transaxle with a limited-slip differential (LSD) assembly to improve vehicle's traction/handling capabilities. However, the LSD assemblies, especially those controlled by a friction clutch, are difficult to integrate into the FWD transaxle unit due to the packaging constraints.
Recently, a great deal of development effort has been directed at packaging the PTU into the FWD transaxle of the conventional FWD vehicles. Known FWD transaxle of the all-wheel drive motor vehicles are susceptible to improvements that may enhance their performance and cost. With this in mind, a need exists to develop an improved FWD transaxle unit of an all-wheel drive motor vehicle that is compact in size, can be packaged into existing front-wheel drive vehicles, and minimizes the FWD transaxle unit redesign, tooling and manufacturing expenses, thus advancing the art.